Newcastle Falcons have signed lock Uili Kolo'ofai from French side US Colomiers on a two-year contract, while Semisi Taulava will no longer join the club from Worcester Warriors.
A Falcons statement said Taulava had failed a medical, and Tonga international Kolo'ofai, also 31, would take his place on the 2014-15 roster.
Kolo'ofai played for Otago and in Japan and Italy before a 2012 move to France.
"He is a versatile forward," Falcons director of rugby Dean Richards said.
"I like what I have seen of him to date and expect him to increase the competition for places in the second and back rows, which will in turn drive forward the standards within the squad."
Worcester have confirmed Taulava is now a free agent following the expiry of his contract, while Newcastle said they will make no further statement on the collapse of the deal.
Meanwhile, Falcons have appointed former Sale and Wigan rugby league commercial director Mick Hogan as managing director.
Hogan had been working as a commercial consultant at Kingston Park.